Computer Networking · Advanced level

Advanced level · Module 3: Network Security and Remote Access · Lesson 1 of 4

Firewalls and Access Control Lists

Allow only the traffic the organisation needs.

In this lesson you will

  • Write a firewall policy
  • Configure and test ACLs

Key concepts

stateful firewallsACLsrule orderdefault deny

The lesson

Stateful firewalls track connections so replies to allowed traffic are permitted automatically. Rules are checked in order; the first match wins.

Start from default deny between zones and allow specific traffic: staff to servers on needed ports, guests to the internet only.

Document each rule's purpose and owner and review rules regularly to remove old ones.

Step by step

  1. Define zones.
  2. Write rules between zones.
  3. Configure ACLs.
  4. Test allowed and blocked traffic.

Practice activity

Implement and test the firewall policy in the lab.

Expected result: A documented policy proven by tests.

Check your understanding

  1. In an ordered rule list, which rule applies?

    Show answer

    The first matching rule.

  2. Why test blocked traffic?

    Show answer

    To prove the policy really blocks it.

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